Urethane foams with reduced smoke levels

ABSTRACT

THIS INVENTION REALTES TO FIRE-RETARDANT POLYURETHANE FOAMS HAVING REDUCED SMOKE LEVELS. THE INVENTION COMPRISES INCORPORATING ADIPIC ACID INTO A FIRE-RETARDANT FOAM FORMULATION.

United States Patent US. Cl. 260-25 AJ 20 Claims ABSTRACT OF THEDISCLOSURE This invention relates to fire-retardant polyurethane foamshaving reduced smoke levels. The invention comprises incorporatingadipic acid into a fire-retardant foam formulation.

STATE OF THE ART Increasing attention has been placed on the amount ofsmoke generated from fire retardant polyurethane foams. It is evidentthat even a polyurethane foam having a low flame spread may create ahazard if the smoke released when the foam is in contact with the flameis sufficient to trap occupants in an enclosed space by obscuring theirvision or hampering their ability to breathe. Methods have beendeveloped for measuring this amount of smoke evolved, for example, seeJournal of Cellular Plastics, January 1967, pages 41-43. Likewise, theUnderwriters Laboratory has developed tests and ratings for measuringsmoke evolution. (For example, ULE84 tunnel tests, as well as UL723.)

DESCRIPTION OF THE INVENTION It has now been found that adipic acid,when incorporated into a phosphorus-containing polyurethanefire-retardant foam formulation greatly reduces the amount of smokegenerated by the foam without substantially detracting from the foamproperties. This is surprising since most aliphatic acids as a class areeither ineffective in reducing smoke generation or significantly degradefoam properties. The amount of adipic acid employed in the foams of thisinvention is that amount which is an effective smoke diminishing amount.Generally about 5 percent to about 40 percent by weight of the totalcomposition is employed. Preferably, about to about percent by weight ofthe total composition is employed.

The polyurethane foams of this invention having reduced smoke generationare virtually any fire-retardant foam formulation formed by reacting anorganic polyisocyanate with an active hydrogen containing material, and

7 containing a phosphorus fire retardant.

The active hydrogen material may be virtually any activehydrogen-containing material employed as a urethane reactant, such as anorganic polyol. Preferably the active hydrogen-containing material is anorganic compound or resin having an isocyanate equivalent between about70 and about 280. The presently preferred groups are polyether polyolshaving a hydroxyl value between about 200 and about 800, such as thereaction product of a polyhydroxyl compound containing 3 to 8 hydroxylgroups and an alkylene oxide containing 2 to 4 carbon atoms. Mostpreferably, the polyether polyol consists essentially of carbon,hydrogen and oxygen.

The reactive hydrogen-containing compounds which are conventionallyemployed in preparing polyurethane foams include as a chief classvarious long-chain aliphatic polyols, polyether polyol, polyesterpolyols and the like. Aliphatic polyols useful in this invention includethose diols which are separated by a carbon chain of 6 to 20 or morecarbon atoms. Since such diols are only difunctional, they areordinarily included only as minor amounts as a reactant in foamformulations designed to produce the novel rigid foams of thisinvention. For purposes of this invention, minor amounts of aliphaticdiols may be defined as amounts which do not detract from the rigidityof the cured foam nor detract from the excellent dimensional stabilityof the foam.

Aliphatic triols such as hexanetriol and polyether polyols prepared bythe oxyalkylation of said aliphatic triols, may be' used in minor ormajor quantities in the foam formulation of this invention. It ispreferred, however, that additional reactive hydrogen components be morethan trifunctional and that the trifunctional polyols and polyetherpolyols be used in relatively minor quantities. The aliphatic triolswhich may be included as an additional reactive hydrogen componentinclude aliphatic triols having 6 or more carbon atoms. Typical triolsinclude the following: trimethylolethane, trimethylolpropane, glycerol,1,2,6- hexanetriol and the like. The trifunctional polyether polyolsuseful in the preparation of rigid polyurethane foams have a hydroxylnumber in excess of about 200 and preferably should have a hydroxylnumber in excess of about 300.

Tetrafunctional polyether polyols and polyether polyols of higherfunctionality are prepared by the reaction of an alkylene oxide, such asethylene oxide, propylene oxide or butylene oxide, with a polyol having4 or more available hydroxyl groups. Typical tetrafunctional and higherfunctional polyether polyol are prepared by the oxyalkylation of polyolssuch as the following: pentaerythritol, sucrose,2,2,6,6-tetrakis(hydroxymethyl)cyclohexanol, glucose, sorbitol,mannitol, degraded starches, degraded cellulose, diglycerol, a-methylglucoside and the like. When such polyether polyols are utilized in thenovel rigid polyurethane foams of this invention, they should have ahydroxyl number in excess of about 200 and preferably in excess of about250, with the best results ordinarily being achieved from thosepolyether polyols having hydroxyl numbers in excess of about 300.

In addition to the aliphatic polyols and the polyether polyols,polyester resins containing hydroxyl groups may be utilized to prepareuseful rigid polyurethane foams. Suitable polyester resins may beprepared by reacting an excess of polyol with a polycarboxylic acid,especially dicarboxylic acids. Typical polyols include: ethylene glycol;propylene glycol; butylene glycol; glycerol; trimethylolpropane;trimethylolethane; 1,2,6-hexanetriol; pentaerythritol; diethyleneglycol; dipropylene glycol; and the like. Typical dicarboxylic acidsinclude: adipic acid, succinic acid, azaleic acid, phthalic acid,isophthalic acid, terephthalic acid, chloroendic acid,tetrabromophthalic acid and the like, and the corresponding anhydrideswhere such anhydrides exist. Also, long chain dimer acids may be used toform useful polyols by esterification with polyols, especially diolssuch as ethylene glycol and the like. For the purposes of thisinvention, useful polyesters should have a minimum hydroxy number ofabout 200, and preferably above about 250, with best results beingobtained from those polyesters having hydroxy numbers in excess of about300.

Another useful class of polyols which can be employed are thetrialkanolamines which, by reaction with alkylene oxides, form adductsof suitable molecular weight, and the alkylene oxide adducts thereof.Illustrative of the lower molecular weight trialkanolamines includetriethanolamine triisopropanolamine and tributanolamine. The alkyleneoxide adducts which can be employed are preferably those wherein theoxyalkylene moieties thereof have from 2 to 4 carbon atoms.

Another useful class of polyols which can be employed are the alkyleneoxide aducts of monoand polyamines and also ammonia. These may be termedaminic polyols.

The monoand polyamines are preferably reacted with alkylene oxides whichhave 2 to 4 carbon atoms, for example, ethylene oxide; 1,2-epoxypropane,the epoxybutanes; and mixture thereof. Monoand polyamines suitable forreaction with alkylene oxides include, among others, methylamine,ethylarnine, isopropylamine, butylamine, benzylamine, aniline, thetoluidines, naphthylamines, ethylenediamine, diethylenetriamine,triethylenetetramine, 1,3-butanediamine, 1,3-propanediamine, 1,4-butanediamine, 1,2-, 1,3-, 1,4-, 1,5- and 1,6-hexanediamine,phenylenediamines, toluenediamine, naphthalenediamines and the like.Among the compounds of the above groups which are of particular interestare, among others, N,N,N',N-tetrakis 2-hydroxyethyl ethylenediamines; N,N,N',N'-tetrakis 2-hydroxypropyl ethylenediamine; N,N, N',N' pentakis(2hydroxypropyl)diethylenetriamine; phenyldiisopropanolamine and higheralkylene oxide adducts of aniline, and the like. Others which deserveparticular mention are the alkylene oxide adducts of aniline orsubstituted aniline/formaldehyde condensation products.

Other active hydrogen-containing materials which may be persent in thenovel urethane foams of this invention include phenol-formaldehydecondensation products, aminic compounds such as diethanolamine,triethanolamine and the like. Another material which may be present inthe foams of this invention is castor oil and its derivatives. Alsouseful are the oxyalkylation products of polyaminepolyamide compounds asobtained by the reaction of dicarboxylic acids with polyamines.

It is obvious that where the active hydrogen compound contains halogenssuch as chlorine or bromine or nitrogen, since these elements contributeto fire retardancy, a lesser amount of phosphorus compound may benecessary than where the active hydrogen-containing material consistsessentially of carbon, hydrogen and oxygen.

Organic polyisocyanates which are reacted with the active hydrogencompounds to form polyurethane foams include the following:

Toluene diisocyanate Chlorophenyl-2,4-diisocyanate Ethylene diisocyanate1,4-tetramethylene diisocyanate Para-phenylene diisocyanateHexamethylene diisocyanate and the like. While the above diisocyanatesmay be reacted with the active hydrogen-containing material to formfoams, it is preferred to form prepolymers of said diisocyanates whenthey are to be used in rigid foam formulations.

When it is desired to form polyurethane foams directly from an organicpolyisocyanate and the active hydrogen-containing materials withoutfirst preparing a prepolymer, it is preferred that poly-nuclearpolyisocyanates of the following type be included:

Diphenyl diisocyanate Triphenyl diisocyanate3,3'-dimethyl-4,4'-biphenylene diisocyanate3,3-dimethoxy-4,4-biphenylene diisocyanate Polymethylene polyphenylisocyanate Diphenylmethane-4,4'-diisocyanate Triphenylmethanetriisocyanate 1,5-naphthalene diisocyanate3,3'-dirnethyldiphenylmethane-4,4-diisocyanate and the like. Of thepreferred polyisocyanates, it has been found that the best results havebeen obtained when the polymeric polyisocyanates having a functionalitygreater than 2.0 are utilized. Exemplary polymeric polyisocyanatesinclude the following:

Crude diphenylmethane 4,4 diisocyanate, commonly referred to as crudeMDI having a functionality of about 2.5 to 2.6. Furthermore, althoughsolid organic polyisocyanates can be utilized in the instant inventionby 4 melting them prior to reaction with other foam-forming ingredients,it is preferred that liquid organic polyisocyanates be utilized.

Another organic polyisocyanate particularly useful is crude tolylenediisocyanate, commonly referred to as crude TDI, containing aboutpercent TDI and about 15 percent polymeric isocyanato and having afunctionality of about 2.1.

Polymethylene polyphenyl isocyanate, referred to as PAPI, having anisocyanate functionality greater than about 2.4, has been found to beparticularly useful.

Polyurethane foams are prepared by reacting approximately one equivalentof active hydrogen-containing resin with one equivalent of an organicpolyisocyanate. It is frequently desirable to include a small amount ofsuitable urethane catalyst and there is also ordinarily included in foamformulations suitable emulsifiers and blowing agents.

The relative amount of organic isocyanato utilized in polyurethane foamformulations is susceptible to variation over a substantial range.Usually the isocyanate component is employed in an amount which providesapproximately one reactive isocyanato group for each reactive hydrogenof the other compound, which is conventionally a polyol, polyamine orsimilar reactive hydrogen-containing material. However, some of theorganic polyisocyanates tend to evaporate and it may be desirable tocompensate for this loss. A range of about one-half equivalent to abouttwo equivalents of organic polyisocyanate per equivalent of polyolcomponent in the final material is ordinarily used, but smaller orlarger amounts can be utilized with good results.

To promote the polyurethane linkage reactions in the final curing of thepolyurethane resins, catalysts are usually required. These includetertiary amines of hydroxyl amines, organic salts of tin, and the like.The following constitutes a partial list of such catalysts:Tetramethylethylenediamine (anhydrous) (TMEDA) Tetramethyl guanidine(TMG) Tetramethyl-l,3butanediamine (TMBDA) Triethylenediamine of theformula:

Dimethylethanolamine (DMEA) Tin esters, such as Stannous oleate Stannousoctoate Dibutyl tin dilaurate Dibutyl tin diacetate and the like.

Many other catalysts may be substituted for those listed above, ifdesired. The amount of catalyst used may be in a range of about 0.05percent to about 5 percent or more by weight based upon the total of thepolyols employed. Mixtures of the above and/or other catalysts may alsobe utilized.

To impart a foamed or cellular structure to the blendedpolyol-polyisocyanate mixture, a suitable gassing agent or system ofgassing agents must be added or produced in situ. The liquid butrelatively volatile halocarbons, such as the following perhalocarbonscontaining 1, 2 or even up to 4 carbon atoms, are especially desirablefor the purpose. These include the following.

The halocarbons having one and two carbon atoms are preferred, and ofthese, trichloromonofiuoromethane and dichlorodifluoromethane areparticularly useful in commercial preparations. These are added asliquids in quantities of about 10 percent or less to about 20 percent ormore, by weight of the total resin to the blended polyolpolyisocyanatemixtures, or to one or more components thereof, and are substantiallyvolatilized in the liquid mixture to effect cellulation. Subsequently,the mixture cures to a hardened, cellular state.

Although the halocarbons are especially desirable as blowing agents whenexceptional insulative properties are desired, such as water, carbondioxide, and the like, can be utilized in this invention.

In order to obtain relatively uniform distribution of the variouscomponents of the liquid system and to achieve proper cellulation, anemulsifier and/or surfactant may be incorporated into the mixture. Thesematerials are physical in their effect and are not always necessary,especially if denser foams are desired. Many hundreds of these areavailable as commercial products. Some of these are listed in thepublication Detergents and Emulsifiers-Up to date, published by John W.McCutcheon, Inc., 475 Fifth Avenue, New York, NY.

Examples of surfactants which may be used include the so-calledPluronics, which have been described as being condensates of ethyleneoxide with a hydrophobic base formed by condensing propylene oxide withpropylene glycol. These are of a molecular weight in a range of about2000 to about 8000 and are ascribed the structure:

Another class of surfactants comprises the so-called Tetronics, whichare formed by the addition of propylene oxide to ethylene diamine,followed by the addition of ethylene oxide. These compounds have beenascribed the structure:

Another valuable class of surfactants comprises the so-called Twcens,which are described as the monoesters of higher fatty acids, representedby lauric acid, stearic acid and oleic acid, and polyoxyethylenesorbitan.

Another of the more satisfactory surfactants which has been found veryeffectively to maintain the cell structure in the foaming and curing ofpolyurethane resins comprises soluble, liquid derivatives of thesilicones. One such product is of the approximate structure:

in which R and R" are monovalent hydrocarbon radicals, while R is adivalent hydrocarbon radical; p, q and r are integers equal to at least1 and may be considerably higher, e.g., 2, 3, 4, 5, 6 or a higher numberup to about 20; n is a whole number from about 2 to about 4; and z is aninteger equal to at least 5 and may be higher, e.g., 6, 7, 8, 9, or evenhigher, up to about 25. One such material is sold as Dow-Corning 199.Still another highly useful silicon base surfactant comprises theso-called silicon L-521, represented by the following formula:

atively dense foams, for example, those weighing about 5 or 6 pounds andupward per cubic foot, the surfactants may be omitted entirely.

The foams employed in the composition of this invention are foams whichare self-extinguishing under the standards set forth in ASTM D-1962-59T.Generally, the minimum amount of phosphorus is about 0.5 to about 2.0percent depending on the formulation.

The phosphorus which contributes to fire-retardancy may be in the formof a reactive or a non-reactive phosphorus-containing compound. Thereactive phosphoruscontaining compound may either be a phosphoruscompound containing active hydrogen groups such as a polyol or may be aphosphorus-containing isocyanate. The nature of the phosphorus compoundis, in fact, the nature of the active hydrogen compound or theisocyanate generally. It is in no manner critical and all such materialsconventionally employed in the art may be employed in the foams of theinvention. A great many phosphorus-containing materials which may beincorporated in the polyurethane foams to achieve fire-retardancy areknown in the art. These materials can be found, for example, in the US.Patent Classification Class 260, subclass 2.5. To enumerate at lengthall the possible materials is deemed unnecessary since one need merelyrefer to the art to determine what materials are available. Thephosphorus-containing polyols include those derived from phosphorus,phosphonic, phosphoric, and pyrophosphoric acids The polyols of theseacids may be prepared ina number of ways such as reacting the acids withalkylene oxides, or halogen-substituted alkylene oxides or byesterification of the acids or transesterification of acid esters withpolyalkylene glycols and polyoxyalkylene glycols. One particularlyuseful class of polyols is the product of the oxyalkylation of an acidester formed from oxyacid of phosphorus and a monohydric alcoholdescribed in U.S. Pat. No. 3,407,150. Other polyols which may beemployed include diethy1-N,N-diethanolaminomethyl phosphonate (Fryol No.6), bis(hydroxypolypropoxypropyl)-N,N'-diethanolaminomethyl phosphonate,tris(hydroxypropyl) phosphate, tris[octakis(2hydroxypropyl)sucrose]phosphite, tris dipropylene glycol phosphite,tris[tetrakis(2- hydroxypropyl) -x-methyl glycoside] phosphite.

Non-reactive phosphorus fire-retardant agents include tris (chloroethyl)phosphate, tris (chloropropyl) phosphate,tris(2,3-dichloropropyl)phosphate, tris (2,3 dibromopropyl)phosphate,bis(beta-chloroethyl)vinyl phosphate.

Phosphorus-containing polyisocyanates include ethylphosphonicdiisocyanate, 'C H P (O) (NCO) phenylphonous diisocyanate, C H P(NCO)The following examples set forth a presently preferred embodiment. Allparts and percentages in the examples as well as throughout thespecification are by weight unless otherwise indicated.

Example I The polyol employed in this example was a sucrose polyetherpolyol as described in US. Pats. Nos. 3,085,085; 3,153,002 and 3,222,357and elsewhere comprising one mole of sucrose, 0.4 molediethylenetriamine, 14.5 moles of propylene oxide and 4 moles ofethylene oxide with an OH of 470.

The isocyanate employed was Mondur-MR, a p,p'-diphenylmethanediisocyanate with a functionality of 2.5 to 2.6 and an NCO equivalent of133.

The fire-retardant additive wasdiethyl-N,N-diethanolaminomethylphosphonate.

The following masterbatch was prepared:

Parts by weight .Polyol (above) 1731.0 Fire retardant (above) 912.0Silicone surfactant 30.0 Dibutyl tin diacetate 6.0

Trichloromonotiuoromethane 888.0

TABLE I Cream Time Time Level (see (parts) onds) onds) Foam descriptionAll the following foams were made by foam parts of the masterbatch witha blend of 100 parts isocya- Additive mate with levels of acid at 10parts, 30 parts and 50 parts. The masterbatch was at 65 P. and the acblend at 77 F. All foamable mixtures were mixed for 10 seconds.

Foam

Designation Other isocyanates, reactive hydrogen materials andphosphorus compounds such as those described hereinabove can besubstituted for those of the examples. Likewise, the adjuvants such ascellulating agent, emulsifier, catalyst, etc., may be chosen from thoseknown in the art.

According to the provisions of the patent statutes, there are describedabove the invention and what are now considered its best embodiments;however, within the scope of the appended claims, it is understood thatthe invention can be practiced otherwise than as specifically described.

We claim:

1. A polyurethane foam formed by foaming a mixture comprising:

(A) an organic polyisocyanate;

(B) an organic polyol;

(C) a phosphorus-containing fire-retardant organic material in an amountsufiicient to render the final foam self-extinguishing;

(D) a smoke-inhibiting amount of the organic compound adipic acid; and

(E) a cellulating agent.

2. A foam as in claim 1 wherein (B) has an isocyanate equivalent ofabout 70 to about 280; (C) is a material reactive in the foamablemixture; and (D) is present in an amount of about percent to about 40percent by weight of the total composition.

3. A foam as in claim 1 wherein (B) comprises a polyether polyol whichis the reaction product of a polyhydroxyl compound containing 3 to 8hydroxyl groups and an alkylene oxide containing 2 to 4 carbon atoms permolecule.

4. A foam as in claim 3 wherein (B) has a hydroxyl value of about 200 toabout 800; (C) is a material reactive in the foamable mixture; and (D)is present in an amount of about 5 percent to about 40 percent of thetotal composition.

5. A foam as in claim 4 wherein the polyol comprises a sucrose polyetherpolyol.

6. A polyurethane foam as in claim 1 formed from a mixture comprising:

(A) an organic polyisocyanate;

(B) an organic polyol having an isocyanate equivalent between about 70and about 280;

('C) a phosphorus-containing fire-retardant organic material in anamount sufficient to render the final foam self-extinguishing;

(D) a smoke-inhibiting amount of the organic compound adipic acid;

(E) a cellulating agent; and

(F) an emulsifier for the mixture.

7. A foam as in claim 6 wherein (B) comprises a polyether polyol whichis the reaction product of a polyhydroxyl compound containing 3 to '8hydroxyl groups and an alkylene oxide containing 2 to 4 carbon atoms permolecule.

8. A foam as in claim 6 wherein (B) has a hydroxyl value above about250.

9. A foam as in claim 8 wherein (C) is a material reactive in thefoamable mixture.

10. A foam as in claim 8 wherein the polyol comprises a sucrosepolyether polyol.

11. A polyurethane foam formed by foaming a mixture comprising:

(A) an organic polyisocyanate;

(B) an organic polyol;

(C) a phosphorus-containing fire-retardant organic material in an amountsufficient to render the final foam self-extinguishing;

(D) a smoke-inhibiting amount of the organic compound adipic acid; and

(E) a halocarbon blowing agent.

12. A foam as in claim 11 wherein (B) has an isocyanate equivalent ofabout to about 280; (C) is a material reactive in the foamable mixtureand (D) is present in an amount of about 5 percent to about 40 percentby weight of the total composition.

13. A foam as in claim 11 wherein (B) comprises a polyether polyol whichis the reaction product of a polyhydroxyl compound containing 3 to 8hydroxyl groups and an alkylene oxide containing 2 to 4 carbon atoms permolecule.

l4. A foam as in claim 13 wherein (B) has a hydroxyl value of about 200to about 800; (C) is a material reactive in the foamable mixture; and(D) is present in an amount of about 5 percent to about 40 percent ofthe total composition.

15. A foam as in claim 14 wherein the polyol comprises a sucrosepolyether polyol.

16. A polyurethane foam as in claim 11 formed from a mixture comprising:

(A) an organic polyisocyanate;

(B) an organic polyol having an isocyanate equivalent between about 70and about 280;

(C) a phosphorus-containing fire-retardant organic material in an amountsufficient to render the final foam self-extinguishing;

(D) a smoke-inhibiting amount of the organic com- :pound adipic acid;

(E) a hydrocarbon blowing agent; and

(F) an emulsifier for the mixture.

17. A foam as in claim 16 wherein (B) comprises a polyether polyol whichis the reaction product of a polyhydroxyl compound containing 3 to 8hydroxyl groups and an alkylene oxide containing 2 to 4 carbon atoms permolecule.

13. A foam as in claim 16 wherein (B) has a hydroxyl value above about250.

19. A foam as in claim 13 wherein (C) is a material reactive in thefoamable mixture.

20. A foam as in claim 18 wherein the polyol comprises a sucrosepolyether polyol.

References Cited UNITED STATES PATENTS 3,472,800 10/1969 Kuryla 260--2.53,249,562 5/1966 Schoepfle 2602.5 3,391,094 7/ 1968 Childers 260--2.5

OTHER REFERENCES Catalysis of Adiprene L/MDCA Compounds? AdipreneBulletin A31783; Elastomer Chemicals Dept.; Dupont; Wilmington, Del;July 1963.

DONALD E. CZAJA, Primary Examiner C. W. IVY, Assistant Examiner U.S. Cl.X.R.

260-2.5 AM, 2.5 AS, 2.5 AR

